Aspects of the present invention relate to opposed piston engines and, more particularly, to opposed piston engines with particular piston face geometries.
In a conventional single piston engine, fuel is injected more or less axially in the cylinder, from the cylinder head that closes the end of the cylinder. In a conventional engine, the combustion chamber is created by the space between the cylinder head and the top of the piston, and generally takes the form of a recess in the head surface, piston top surface or both. Combustion chamber designs that create effective mixing of the fuel and air for good combustion are well established for conventional engines.
Opposed piston engines are engines in which two pistons are contained within one cylinder, with the combustion chamber formed between the pistons, and therefore there is no cylinder head. When used for a compression ignition engine, fuel is injected from a location that is located more or less radially in the cylinder wall, at the space formed between the pistons. This is referred to as “side injection”. In general, opposed piston engines have traditionally suffered from relatively poor combustion, as it is much more difficult to create a chamber that effectively mixes the air and fuel, resulting in poor soot emissions, smoke, and poorer efficiency than would otherwise be expected.
One major challenge with opposed piston diesel engines is that fuel injection must enter the cylinder from the side of the cylinder, typically roughly perpendicular to the cylinder axis. This is in contrast to conventional engines, where the injection spray is more or less aligned with the cylinder axis, and which allows a combustion chamber that is axisymmetric.
Historically, most opposed piston engines have placed injectors on opposite sides of the engine in order to cause combustion to occur relatively centered in the cylinder. However, there are several disadvantages to this design of injectors on opposite sides of the cylinder. There is a danger of having the spray plumes from both injectors impinge into each other, a condition that is known in modern diesel combustion theory to lead to high soot creation. Most designs that try to keep well centered combustion have this weakness to a larger or smaller extent.
Another disadvantage is related to the fact that high pressure fuel systems are made up of components that are likely to require service during the life of the engine. Having the fuel system on both sides of the engine means that service technicians must have access to both sides of the engine, and move from side to side of the application to perform service work, which can be difficult or at least time consuming on large engines or in commercial vehicle fixed installation applications.
Further, modern high pressure fuel systems contain many delicate components, including wiring connections, high pressure fluid connections, and electrical components inside the fuel injectors. All of these are sensitive to high heat, and may leak fuel during service or in case of a mechanical failure. When injectors are located on both sides of the engine, it is very difficult to isolate the fuel passages and electrical features from close proximity to exhaust manifolds, which are a source of high heat and possible ignition source.
It is desirable to provide an opposed piston engine that provides for fuel injection in a manner that can avoid impingement of fuel spray plumes on each other. It is also desirable to avoid the disadvantages of having injectors on opposite sides of the cylinder.
According to an aspect of the present invention, an opposed piston engine comprises a cylinder having a cylinder wall, a pair of opposed pistons, each piston of the pair of opposed pistons having a face, the pair of pistons being disposed in the cylinder and movable between first positions in the cylinder in which faces of the opposed pistons and the cylinder wall define a maximum volume and second positions in the cylinder in which the faces of the opposed pistons and the cylinder wall define a minimum volume, wherein each face of each piston of the pair of opposed pistons has a top plane and a recess formed therein, each recess comprising a first surface defining part of a cone, the cone defined by the first surface of at least one of the recesses having a longitudinal axis that defines an angle equal to at least one half of a cone angle of the cone with the top plane.